Backscattering of Electrons from Complex Structures

The backscattering of electrons from complex targets (for example, metal layer on a semi-infinite substrate with a polymer resist film above) has been studied both theoretically and experimentally. The experimental structures were exposed with an electron beam in a spot mode . The experimental observations of developed disc radius vs. exposure time and metal layer thickness support the simple theory of scattering in such structures. The theory assumes that the backscattering causes enlarging of the exposed area by a constant value. This value is derived from the proposed scattering model based on the Archard\u27s and Kanaya and Okayama\u27s diffusion theories. The radial exposure intensity distribution introduced by the electron beam has been approximated by a Gaussian function

Comment on "Discrepancies in the resonance-fluorescence spectrum calculated with two methods"

There are two alternative methods used in literature to calculate the incoherent part of the spectrum of light scattered by an atomic system. In the first, one calculates the spectrum of the total light scattered by the system and obtains the incoherent part by subtracting the coherent part. In the second method, one introduces the fluctuation operators and obtains the incoherent part of the spectrum by taking the Fourier transform of the two time correlation function of the fluctuation operators. These two methods have been recognized for years as two completely equivalent for evaluating the incoherent part of the spectrum. In a recent paper Qing Xu et al. [Phys. Rev. A 78, 013407 (2008)] have shown that there are discrepancies between the incoherent parts of the stationary spectrum of a three-level Lambda-type system calculated with these two methods. The predicted discrepancies can be severe that over a wide rage of the Rabi frequencies and atomic decay rates, the spectrum calculated with the variance method can have negative values. This is obviously unphysical result since the fluorescence spectrum is a positively defined quantity. It represents the frequency distribution of light incoherently scattered by the atomic system. Therefore, the calculated spectrum should be positive for all frequencies independent of values of the Rabi frequencies and the damping rates. In this comment, we show that there are no discrepancies between these two methods. The equivalence of these two alternative methods leads to the same incoherent spectra that are positive for all frequencies independent of values of the parameters involved. The analytical analysis is supported by simple numerical calculations.Comment: Comments on the comment are welcom

Effect of retardation on the dynamics of entanglement between atoms

The role of retardation in the entanglement dynamics of two distant atoms interacting with a multi-mode field of a ring cavity is discussed. The retardation is associated with a finite time required for light to travel between the atoms located at a finite distance and between the atoms and the cavity boundaries. We explore features in the concurrence indicative of retardation and show how these features evolve depending on the initial state of the system, distance between the atoms and the number of modes to which the atoms are coupled. In particular, we consider the short-time and the long time dynamics for both the multi- and sub-wavelength distances between the atoms. It is found that the retardation effects can qualitatively modify the entanglement dynamics of the atoms not only at multi- but also at sub-wavelength distances. We follow the temporal evolution of the concurrence and find that at short times of the evolution the retardation induces periodic sudden changes of entanglement. To analyze where the entanglement lies in the space spanned by the state vectors of the system, we introduce the collective Dicke states of the atomic system that explicitly account for the sudden changes as a periodic excitation of the atomic system to the maximally entangled symmetric state. At long times, the retardation gives rise to periodic beats in the concurrence that resemble the phenomenon of collapses and revivals in the Jaynes-Cummings model. In addition, we identify parameter values and initial conditions at which the atoms remain separable or are entangled without retardation during the entire evolution time, but exhibit the phenomena of sudden birth and sudden death of entanglement when the retardation is included.Comment: 16 pages, 14 figure

On the chemical composition of cosmic rays of highest energy

We present arguments aiming at reconciling apparently contradictory results concerning the chemical composition of cosmic rays of highest energy, coming recently from the Auger and HiRes collaborations. In particular, we argue that the energy dependence of the mean value and root mean square fluctuation of shower maxima distributions observed by the Auger experiment are not necessarily caused by the change of nuclear composition of primary cosmic rays. They could also be caused by the change of distribution of the first interaction point in the cascade. A new observable, in which this influence is strongly suppressed, is proposed and tested.Comment: Version accepted by J.Phys. G (2011

Molecular Aspects of Dopaminergic Neurodegeneration: Gene-Environment Interaction in Parkin Dysfunction

Parkinson’s disease (PD) is a common neurodegenerative movement disorder that is characterized pathologically by a progressive loss of midbrain dopaminergic neurons and by protein inclusions, designated Lewy bodies and Lewy neurites. PD is one of the most common neurodegenerative diseases, affecting almost 1% of the population over 60 years old. Although the symptoms and neuropathology of PD have been well characterized, the underlying mechanisms and causes of the disease are still not clear. Genetic mutations can provide important clues to disease mechanism, but most PD cases are sporadic rather than familial; environmental factors have long been suspected to contribute to the disease. Although more than 90% of PD cases occur sporadically and are thought to be due, in part, to oxidative stress and mitochondrial dysfunction, the study of genetic mutations has provided great insight into the molecular mechanisms of PD. Furthermore, rotenone, a widely used pesticide, and paraquat and maneb cause a syndrome in rats and mice that mimics, both behaviorally and neurologically, the symptoms of PD. In the current review, we will discuss various aspects of gene-environment interaction that lead to progressive dopaminergic neurodegenration, mainly focusing on our current finding based on stress-mediated parkin dysfunction

Signal from noise retrieval from one and two-point Green's function - comparison

We compare two methods of eigen-inference from large sets of data, based on the analysis of one-point and two-point Green's functions, respectively. Our analysis points at the superiority of eigen-inference based on one-point Green's function. First, the applied by us method based on Pad?e approximants is orders of magnitude faster comparing to the eigen-inference based on uctuations (two-point Green's functions). Second, we have identified the source of potential instability of the two-point Green's function method, as arising from the spurious zero and negative modes of the estimator for a variance operator of the certain multidimensional Gaussian distribution, inherent for the two-point Green's function eigen-inference method. Third, we have presented the cases of eigen-inference based on negative spectral moments, for strictly positive spectra. Finally, we have compared the cases of eigen-inference of real-valued and complex-valued correlated Wishart distributions, reinforcing our conclusions on an advantage of the one-point Green's function method.Comment: 14 pages, 8 figures, 3 table

Entanglement created by spontaneously generated coherence

We propose a scheme able to generate on demand a steady-state entanglement between two non-degenerate cavity modes. The scheme relies on the interaction of the cavity modes with driven two or three-level atoms which act as a coupler to build entanglement between the modes. We show that in the limit of a strong driving, crucial for the generation of entanglement between the modes is to imbalance populations of the dressed states of the driven atomic transition. In the case of a three-level V-type atom, we find that a stationary entanglement can be created on demand by tuning the Rabi frequency of the driving field to the difference between the atomic transition frequencies. The resulting degeneracy of the energy levels together with the spontaneously generated coherence generates a steady-state entanglement between the cavity modes. It is shown that the condition for the maximal entanglement coincides with the collapse of the atomic system into a pure trapping state. We also show that the creation of entanglement depends strongly on the mutual polarization of the transition atomic dipole moments.Comment: Published versio